Bearing bush system for a two-part steering shaft

ABSTRACT

A bearing bush system includes a bearing bush of polyamide that is held on an outer steering shaft with a stopping collar and on the free face of which the one-piece sealing element of thermoplastic elastomer that seals statically with a ring seal as well as dynamically with sealing lips is held in a form-fitting fashion by means of watchtower-like denticulated ribs provided on both sides. The bearing bush system of two plastics forms a single component, requires low manufacturing expenditures, can be easily assembled and also ensures a reliable seal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of PCT/DE2007/000203 filed onJan. 31, 2007, which claims priority under 35 U.S.C. §119 of GermanApplication No. 10 2006 012 057.4 filed on Mar. 8, 2006. Theinternational application under PCT article 21(2) was not published inEnglish.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to a bearing bush system for a two-part steeringshaft that serves for producing an axially movable and sealingconnection between an outer steering shaft and an inner steering shaftand comprises a bearing bush, static and dynamic sealing means and acovering cap.

2The Prior Art

One known two-part steering shaft for utility vehicles comprises anouter steering shaft that consists of an outer tube and features abearing bush that is integrated into its free end, as well as an innersteering shaft that is realized in the form of an inner tube and guidedin this bearing bush in an axially movable fashion in order tocompensate vibrations that occur during the operation of the vehicle andare transmitted to the steering shaft or to allow a length compensationof the steering shaft when tilting the driver's cab. The bearing bushshould not only allow a free and vibration-damping sliding movement, butalso ensure an adequate outward seal between the two concentricallyarranged parts so as to prevent the admission of splash and washingwater, as well as dirt, dust and sand particles.

In order to mutually seal the two steering shaft parts, it was alreadyproposed to utilize a bearing bush arrangement with a shaft sealattached on the outer face of the bearing bush, wherein the peripheralsealing lip of this shaft seal rests against the surface of the innersteering shaft. The shaft seal is fixed with the aid of an elbowedholding sleeve. The static seal between the bearing bush and thesteering shaft is realized with an O-ring that is arranged between theholding sleeve and the face of the outer steering shaft.

One disadvantage of the proposed solution can be seen in the highmanufacturing costs and assembly expenditures for the bearing brush thatconsists of four individual parts in all. In addition, the O-ring may beexcessively compressed by the holding sleeve such that it loses itselasticity and therefore its sealing effect that is based on thiselasticity.

SUMMARY OF THE INVENTION

The invention is based on the objective of developing a bearing bush fora two-part steering shaft that can be manufactured and assembled withlow expenditures and also has improved sliding and sealing effects.

According to the invention, this objective is attained with a bearingbush that is described in this application.

In other words, the fundamental idea of the invention consists of theform-fitting connection between the bearing bush that is held on theouter steering shaft with a stopping collar and consists of a hardplastic and a one-piece sealing element that is moulded of a flexibleplastic and not only comprises a dynamic lip seal relative to the innersteering shaft, but also a static ring seal for producing the seal onthe face of the outer steering shaft. In order to fix the sealingelement on the face of the bearing bush in a form-fitting fashion,interlocking watchtower-like denticulated ribs are realized on bothsides and also absorb the prestressing force of the holding bush,wherein the denticulated ribs are also anchored within one another dueto the shrinkage that occurs when they cool off. The integrally mouldedstatic ring seal extends over the height of the lateral surface of thestopping collar and therefore has a high elastic sealing effect. Thisbearing bush represents a combination of two plastics that form a singlecomponent, wherein this bearing bush can be manufactured and assembledwith low expenditures and ensures a reliable static and dynamic seal.

In an additional development of the invention, the static seal comprisestwo peripheral sealing lips that are spaced apart and arranged on top ofone another such that a lubricant reservoir is formed therebetween. Thisimproves the sliding properties, as well as the dynamic seal.

In one embodiment of the invention, longitudinal ribs and/or lateralribs are integrally moulded on the outer surface of the bearing bush forreinforcing purposes.

The one-piece sealing element consists of a thermoplastic elastomer thatis supported on or in the denticulated ribs of the preferably polyamidebearing bush and thusly prevented from yielding. The polyamidepreferably contains an internal lubricant such as, for example, Teflonor molybdenum dioxide.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention that also results in other advantageousdesigns of the bearing bush system is described in greater detail belowwith reference to the drawings. In these drawings:

FIG. 1 shows a sectioned perspective representation of a bearing busharrangement that is situated on the outer steering shaft;

FIG. 2 shows an enlarged representation of part of the bearing bushsystem;

FIG. 3 shows a side view of a bearing bush with a statically anddynamically acting sealing element arranged thereon in a self-lockingfashion;

FIG. 4 shows a perspective representation of the bearing bush systemaccording to FIG. 3, however, with the sealing element partially cutaway, and

FIG. 5 shows a bottom view of the sealing element.

DETAILED DESCRIPTION OF THE DRAWINGS

According to FIGS. 1 and 2, a bearing bush 3 is arranged in the interiorof an outer steering shaft 1 and held on a stopping collar 2 with itsface in order to accommodate a (not-shown) inner steering shaft in anaxially movable fashion. The bearing bush 3 consists of a hard firstplastic, namely of polyamide in the embodiment shown, into which aninternal lubricant such as, for example, Teflon or molybdenum dioxide ischemically incorporated. Longitudinal ribs 4 of semicircular crosssection and/or lateral ribs 5 lying therebetween are integrally mouldedon the outer circumference of the bearing bush 3 within regulardistances from one another. First denticulated ribs 6 are provided onthe face of the stopping collar 2 and the bearing bush 3. A sealingelement 7 that also overlaps the lateral surface of the stopping collar2 is fixed on the face of the bearing bush 3 in a form-fitting fashion,namely with the aid of second denticulated ribs 8 that are integrallymoulded on the underside of the sealing element 7 and engage into thegaps between the first denticulated ribs 6.

The sealing element 7 consists of a soft second plastic, i.e., of athermoplastic elastomer (TPE, technical rubber) that shrinks on thebearing bush consisting of the hard plastic when it cools off such thatits (second) denticulated ribs 8 become anchored in the (first)denticulated ribs 6 of the bearing bush 3 and a rigid, intimate, but notrubberized adhesive, connection is produced between the bearing bush 3and the sealing element 7. The pressure acting upon the sealing element7 of soft thermoplastic elastomer is absorbed by the bearing bush 3 andthe denticulated ribs 6 consisting of hard polyamide. The quantity ofthermoplastic elastomer material that is reduced due to the ribstructure also results in a direct support of the sealing element 7 andtherefore suppresses its tendency to yield under high pressure.

The sealing element 7 features an inner limb 9 (lip ring seal) with twoperipheral sealing lips that are spaced apart and arranged on top of oneanother, i.e., a first sealing lip 10 and a second sealing lip 11 with alubricant reservoir 12 formed therebetween. A peripheral outer limbrests against the lateral surface of the stopping collar 2 and, togetherwith its bulge 13 that slightly protrudes over the lateral surface ofthe stopping collar 2 and rests against the face of the outer steeringshaft 1, forms a static ring seal 14 with a large excursion thatcorresponds to the long limb length. This static seal also maintains itselastically sealing effect under very high pressures. In order toincrease the elasticity of the first (upper) sealing lip 11, a groove 15is arranged in the sealing element 7 at the transition to this sealinglip 10. The bearing bush 3 and the sealing element 7 that is rigidlyconnected thereto and features the two dynamic seals forming first andsecond sealing lips 10, 11 and the statically acting ring seal 14collectively form a single first component consisting of two plasticsthat are rigidly fitted together, wherein this first component is fixedon the face of the outer steering shaft 1 by means of a secondcomponent, namely a metallic covering cap 16.

The bearing bush arrangement therefore consists of only two componentsthat can be easily assembled and fulfill five functions, i.e., thefunction of a sliding bearing, of a static seal and of a dynamic sealincluding lubricating effect and attachment. The manufacturing andassembly expenditures for such a bearing bush arrangement consequentlyare low. In addition, the two lip seals and the lubricant reservoir, aswell as a highly elastic static seal, result in a one-piece sealingelement that produces an excellent seal against water under pressure orsplash water, steam, dirt, dust and sand.

In addition, the two plastic parts of the first component are connectedto one another in a form-fitting fashion such that yielding of the softsealing material under the influence of pressure is avoided.

LIST OF REFERENCE SYMBOLS

-   1 Outer steering shaft-   2 Stopping collar-   3 Bearing bush-   4 Longitudinal ribs-   5 Lateral ribs-   6 First denticulated ribs, see 3-   7 Sealing element-   8 Second denticulated ribs, see 7-   9 Inner limb/dynamic lip seal, see 7-   10 First sealing lip-   11 Second sealing lip-   12 Lubricant reservoir-   13 Bulge-   14 Static ring seal-   15 Groove-   16 Covering cap

1. A bearing bush system for a two-part steering shaft that serves forproducing an axially movable and sealing connection between an outersteering shaft and an inner steering shaft, the bearing bush systemcomprising: a bearing bush; a one-piece static and dynamic sealingelement; and a covering cap; wherein the bearing bush has a face,comprises a hard plastic, is provided with a stopping collar, and isconnected on the face to the one-piece static and dynamic sealingelement; wherein the one-piece static and dynamic sealing elementcomprises flexible plastic material and seals statically and dynamicallyvia a shrink denticulation, the shrink denticulation interlocking in aform-fitting fashion and simultaneously supporting the flexible plasticmaterial; wherein a peripheral inner limb of the one-piece static anddynamic sealing element is provided as a dynamic seal and features afirst sealing lip; and wherein a peripheral outer limb of the one-piecestatic and dynamic sealing element overlaps a lateral surface of thestopping collar, contacts the face of the outer shaft, and acts as astatic ring seal.
 2. The bearing bush system according to claim 1,wherein the shrink denticulation comprises first and second denticulatedribs arranged on the one-piece static and dynamic sealing element and onthe bearing bush; and wherein the first and second denticulated ribs aremechanically anchored in one another due to the shrinkage that occurswhen the flexible plastic material cools off.
 3. The bearing bush systemaccording to claim 1, wherein a second peripheral sealing lip isarranged at a distance from the first sealing lip such that the secondperipheral and first sealing lips enclose a lubricant reservoir.
 4. Thebearing bush system according to claim 1, wherein a peripheral groove isarranged in the one-piece static and dynamic sealing element at atransition to the peripheral inner limb.
 5. The bearing bush systemaccording to claim 1, wherein the static ring seal of the one-piecestatic and dynamic sealing element features a free face and a bulge onthe free face, the bulge protruding over the lateral surface of thestopping collar and contacting the steering shaft.
 6. The bearing bushsystem according to claim 1, wherein longitudinal ribs and/or lateralribs of semicircular cross section are integrally molded on an outersurface of the bearing bush.
 7. The bearing bush system according toclaim 1, wherein the hard plastic used for the bearing bush comprisespolyamide with a chemically incorporated internal lubricant.
 8. Thebearing bush system according to claim 7, wherein the chemicallyincorporated internal lubricant comprises Teflon or molybdenum dioxide.9. The bearing bush system according to claim 1, wherein the flexibleplastic material used for the one-piece static and dynamic sealingelement comprises a thermoplastic elastomer.